[string] Add a fast path to String.p.replace

src/runtime/runtime-strings.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/runtime/runtime-utils.h"
 
 #include "src/arguments.h"
 #include "src/conversions.h"
 #include "src/counters.h"
 #include "src/objects-inl.h"
 #include "src/regexp/jsregexp-inl.h"
 #include "src/string-builder.h"
 #include "src/string-search.h"
 
 namespace v8 {
 namespace internal {
 
 RUNTIME_FUNCTION(Runtime_GetSubstitution) {
   HandleScope scope(isolate);
-  DCHECK_EQ(4, args.length());
+  DCHECK_EQ(5, args.length());
   CONVERT_ARG_HANDLE_CHECKED(String, matched, 0);
   CONVERT_ARG_HANDLE_CHECKED(String, subject, 1);
   CONVERT_SMI_ARG_CHECKED(position, 2);
   CONVERT_ARG_HANDLE_CHECKED(String, replacement, 3);
+  CONVERT_SMI_ARG_CHECKED(start_index, 4);
 
   // A simple match without captures.
   class SimpleMatch : public String::Match {
    public:
     SimpleMatch(Handle<String> match, Handle<String> prefix,
                 Handle<String> suffix)
         : match_(match), prefix_(prefix), suffix_(suffix) {}
 
     Handle<String> GetMatch() override { return match_; }
     Handle<String> GetPrefix() override { return prefix_; }
@@ skipping 16 matching lines @@
     Handle<String> match_, prefix_, suffix_;
   };
 
   Handle<String> prefix =
       isolate->factory()->NewSubString(subject, 0, position);
   Handle<String> suffix = isolate->factory()->NewSubString(
       subject, position + matched->length(), subject->length());
   SimpleMatch match(matched, prefix, suffix);
 
   RETURN_RESULT_OR_FAILURE(
-      isolate, String::GetSubstitution(isolate, &match, replacement));
+      isolate,
+      String::GetSubstitution(isolate, &match, replacement, start_index));
 }
 
 // This may return an empty MaybeHandle if an exception is thrown or
 // we abort due to reaching the recursion limit.
 MaybeHandle<String> StringReplaceOneCharWithString(
     Isolate* isolate, Handle<String> subject, Handle<String> search,
     Handle<String> replace, bool* found, int recursion_limit) {
   StackLimitCheck stackLimitCheck(isolate);
   if (stackLimitCheck.HasOverflowed() || (recursion_limit == 0)) {
     return MaybeHandle<String>();
@@ skipping 681 matching lines @@
   SealHandleScope shs(isolate);
   DCHECK_EQ(2, args.length());
   if (!args[0]->IsString()) return isolate->heap()->undefined_value();
   if (!args[1]->IsNumber()) return isolate->heap()->undefined_value();
   if (std::isinf(args.number_at(1))) return isolate->heap()->nan_value();
   return __RT_impl_Runtime_StringCharCodeAtRT(args, isolate);
 }
 
 }  // namespace internal
 }  // namespace v8